Cyclosporin A inhibits T cell receptor‐induced interleukin‐2 synthesis of human T lymphocytes by selectively preventing a transmembrane signal transduction pathway leading to sustained activation of a protein kinase C isoenzyme, protein kinase C‐β

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Abstract
Stimulation of human peripheral blood lymphocytes via T cell receptor/CD3 complex resulted in a bimodal activation of protein kinase(s) C (PKC). Within 10 min of stimulation PKC‐α was translocated to, and thus activated in, the plasma membranes of human lymphocytes, followed by a fast dissociation of this isotype from the plasma membrane. This short term activation and translocation PKC‐α proved to be cyclosporin A (CsA) insensitive. After 90 min of stimulation PKC‐β was translocated to and remained bound to the plasma membranes for up to 4 h. Preincubation of human lymphocytes with 200 ng/ml CsA specifically and completely abolished the sustained activation of PKC‐β. Neither the phorbol ester‐induced direct activation of PKC nor the specific activity of the plasma membrane‐bound enzyme was influenced by CsA, suggesting that a signal transduction pathway leading to sustained activation of PKC‐β was influenced by the immunosuppressive agent. In fact, CsA inhibited, in a concentration‐dependent manner, the activation of lysophosphatid acyltransferase‐catalyzed elevated incorporation of cis‐polyunsaturated fatty acids into plasma membrane phospholipids. While interleukin‐2 (IL‐2) synthesis and cellular proliferation were completely inhibited by 200 ng/ml CsA in BMA 030‐ or BMA 031‐stimulated cells, expression of high‐affinity IL‐2 receptors was not influenced by the immunosuppressive drug. These results suggest that synthesis and expression of high‐affinity IL‐2 receptors might be regulated by a signal‐transducing pathway involving activation and translocation of PKC‐α. Lysophosphatid acyltransferase‐catalyzed incorporation of cis‐polyunsaturated fatty acids might represent another mechanism of signal transduction implicated in the activation and translocation of PKC‐β, which is specifically inhibited by CsA. Neutralization of PKC‐β by introducing anti‐PKC‐β antibodies prevented IL‐2 synthesis and proliferation in stimulated human lymphocytes. The results suggest a possible link between activation of PKC‐β and regulation of IL‐2 synthesis in activated human lymphocytes. Thus, inhibition of the activation and translocation of PKC‐β by CsA may result in inhibition of IL‐2 gene expression in human lymphocytes.